As a thin type printed circuit board, the printed circuit board as disclosed in, for example, Japanese Unexamined Patent Publication No. 2002-43752 has heretofore been known in which a plurality of tapered through holes are formed in a thin insulating layer, and these through holes are filled with a plated conductor, and wiring conductors formed from the same plated conductor are respectively formed on upper and lower surfaces of the insulating layer.
In this printed circuit board, however, the plated conductor applied to the inside of the through hole, and the wiring conductors formed on the upper and lower surfaces of the insulating layer are formed from the same plated conductor. Therefore, the formation of the plated conductor thick enough to fill these through holes involves the formation of a thick plated conductor having a thickness of approximately 40 μm on each of the upper and lower surfaces of the insulating layer. This is because the plated conductor, of which thickness is the same as that of the plated conductor deposited inside of the through hole for applying to the inside of the through hole, is deposited on each of the upper and lower surfaces of the insulating layer at the same time. Thus, when the plated conductor formed on each of the upper and lower surfaces of the insulating layer has a thickness of approximately 40 μm, it is necessary to set so that the width of the wiring conductor, which is in the direction parallel to the upper and lower surfaces of insulating layer and is also perpendicular to the direction the wiring conductor extends, formed from the plated conductor is approximately 50 μm, and the spatial interval between the adjacent wiring conductors is approximately 60 μm in consideration of the plated conductor thickness and an anchor depth. It is therefore difficult to arrange the wiring conductors having a smaller width than approximately 50 μm at narrower spatial intervals than approximately 60 μm.
Consequently, the conventional method of manufacturing the printed circuit board is not capable of achieving the thin type printed circuit board having high density wiring in which, for example, the width of the wiring conductors and the spatial interval between the adjacent wiring conductors are 30 μm or less.